1. Field of the Invention
This invention relates to methods and micro power generators for generating electrical power from low frequency vibrational energy.
2. Background Art
The following references are referenced herein:                [1] B. Koenaman et al., “Feasibility of Micro Power Supplies for MEMS,” JMEMS, Vol. 6, No. 4, pp. 355-362, December 1997.        [2] M. Mizuno et al, “Investigation of a Resonance Microgenerator,” J. OF MICROMECH. MICROENG., Vol 13, pp. 209-216, 2003.        [3] S. Meninger et al. “Vibration-to-electric Energy Conversion,” IEEE TRANS. ON VLSI SYSTEMS, Vol. 9, No. 1, pp. 64-76, 2001.        [4] C. B. Williams et al., “Analysis of a Micro-electric Generator for Microsystems,” SENS. AND ACTUATORS A, Vol. 52, pp. 8-11, 1996.        [5] C. B. Williams, R. C. Woods, and R. B. Yates, “Feasibility Study of a Vibration Powered Micro-electric Generator,” IEEE COLLOQUIUM ON COMPACT POWER SOURCES, pp. 7/1-7/3, May 1996.        [6] R. Amirtharajah, S. Meninger, J. O. Mur-Miranda, A. Chandrakasan, J. Lang, “A Micropower Programmable Dsp Powered Using a MEMS-based Vibration-to-electric Energy Converter,” DIGEST OF TECHNICAL PAPERS ISSCC 2000, pp. 362-363, February 2000.        [7] S. Meninger, J. O. Mur-Miranda, R. Amirtharajah, A. Chandrakasan, J. Lang, “Vibration-to-electric Energy Converter,” IEEE INTERNATIONAL SYMPOSIUM ON LOW POWER ELECTRONICS AND DESIGN, pp. 48-53, August 1999.        [8] R. Amirtharajah, A. P. Chandrakasan, “Self-powered Signal Processing Using Vibration-based Power Generation,” IEEE JOURNAL OF SOLID-STATE CIRCUITS, Vol. 33, No. 5, pp. 687-695, 1998.        [9] R. Amirtharajah, A. P. Chandrakasan, “Self-powered Low Power Signal Processing,” IEEE SYMPOSIUM ON VLSI CIRCUITS, pp. 25-26, 1997.        [10] S. G. Kelly, “Fundamentals of Mechanical Vibrations,” Chapter 3, McGraw-Hill, 1997.        [11] H. Hosaka et al., “Evaluation of Energy Dissipation Mechanism in Vibrational Microactuators,” MEMS '94, pp. 193-198, 1994.        
Self-powered remote controlled microsystems are needed in many emerging applications including environmental monitoring and military applications. The required power for these systems can be generated mainly in two ways: 1) by using electrochemical batteries and micro fuel cells; and 2) by energy scavenging from environmental sources such as ambient heat, light, and vibration. Although electrochemical batteries and micro-fuel cells can provide more power, they are not desirable for some applications due to chemicals and reactions involved during the generation process. Also, they have a limited life time.
Energy scavenging from ambient sources has become popular recently, because of its clean power generation process and long life-time.
Among the other environmental energy scavenging sources, vibration is particularly attractive because of its abundance, and several scavenging techniques based on piezoelectric, electrostatic and electromagnetic transduction have been reported [1-9]. The maximum voltage and generated electrical power from a vibrating mass is strongly dependent on the external vibration frequency [4], and drops dramatically at low frequencies (1-10 Hz). But it is at these low frequencies where most ambient vibration exists. FIG. 1 shows the maximum power from an electromagnetic generator vs vibration frequency. In FIG. 1, it is assumed that the applied external vibration matches the generator resonance frequency. Most reported devices are only capable of operating at frequencies of several kHz; at lower frequencies they are ineffective.
Published U.S. patent application 2004/0007942 discloses an integrated MEMS resonant generator system including a plurality of piezoelectric microgenerators which generate a voltage in response to vibrational energy.
Consequently, there is a need for a method and micro power generator for converting vibrational energy having an ambient, relatively low frequency to electrical power.